Hesperogaulus, a new genus of mylagaulid rodent (Mammalia) from the Miocene (Barstovian to Hemphillian) of the Great Basin

A new genus of mylagaluid rodent from the Miocene of the Great Basin, Hespe rogaulus, is described, and to it two new species, H. gazini and H. wilsoni (type species) are referred. This genus differs from all other genera of l ater Tertiary mylagaulines in having: large bosses of rugose bone on the an terior end of the nasal bones; lower slope of the occipital bone; and uniqu e separation of the anterior branches of the forked parafossette on the upp er premolar. Hepserogaulus n. gen. represents a distinct lineage of mylagaulids that has been separate from other members of the family since the early Barstovian. This genus is geographically limited to the Great Basin. Other later Terti ary genera of mylagaulids show geographic limitations to other parts of the continent as well.